Electrical propulsion systems for vehicles such as bicycles, tricycles, go-carts, wheel chairs and the like suffer from a limitation in energy storage capabilities of the electrical storage cells used to propel such vehicles. One reason for this is that these vehicles are controlled very inefficiently, the drive system being activated unnecessarily when very modest manual effort would easily propel such a vehicle, and the braking being accomplished by frictional means such that the kinetic energy of the vehicle is not recovered. This invention overcomes this undesirable limitation in such relatively light weight vehicles by using battery assistance in propelling the cycle only when assistance is required to prevent excessive effort by the cycle operator. Such battery-assistance is achieved by employing a sensor that automatically senses the tension of the chain that drives the rear wheel of a cycle during pedalling. In a specific, and serving only as an exemplary, technique for achieving such sensing, a spring-loaded unit in conjunction with an optical interrupter module is employed. The interrupter module acts as a variable resistor to control the duty cycle of a multivibrator, the latter being amplified by suitable pulse circuitry to drive a motor that is linked independently of the chain system to a wheel of the vehicle.
By appropriately adjusting such sensor and pulse circuitry, the motor, during pedalling on flat or level surfaces, will be energized only enough so that it can overcome frictional losses in the drive system. When the pedaller must climb a hill or drive against a strong wind, he must apply greater force to the pedals, and such greater force increases the tension on the drive chain, which increased tension is sensed by the spring-loaded unit and optical system.
The sensed tension increase is translated into an increased motor duty cycle, thus reducing the pedaller's efforts during the hill-climbing or strong head-wind interval. This use of the driving motor only when needed greatly increases the life of the battery.
When the pedaller wishes to brake the vehicle, this is accomplished either by the depression of hand levers or by reversing the direction of pedalling. The reversed tension in the chain or the tension in the linkage operated by the hand levers is sensed by a sensor similar to that described for controlling power to the motor. The sensed tension is translated into a sequence of pulses which short the motor terminals for brief periods of time. The large currents which develop in the motor windings cause braking action, and, as a result of the nature of the shorting action and control circuit, repetitively decay through the battery, thereby recharging the battery.
Consequently, it is a principle object of this invention to provide a manually operated vehicle with an electric motor that will automatically assist an operator of said vehicle during those periods when extra exertion is needed to propel the vehicle, which extra exertion is either uncomfortable or exceedingly difficult to achieve.
It is yet another object to provide an electronic circuit that is compatible with the electric motor to be used on such a cycle so as to preserve the life of the battery operating such motor.
It is yet another object to provide a regenerative braking system that is controlled by action of the normal braking unit on the bicycle so as to provide a smooth and controlled braking action.
Further objects and advantages of the invention will become apparent as the following description proceeds, and the features of novelty which characterize this invention will be pointed out with particularity in the claims annexed to and forming part of this specification.